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Running 87 Octane when 93 Octane is specified
I'm thinking about buying a 1999-2005 gas Mercedes. I think I remember reading that Mercedes specifies using 91 or 93 octane premium.
Has anyone tried to run 87 (regular) octane gas in these cars? What is the performance difference? Does it "hurt" the engine or does the computer compensate for the difference?
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Pete Williams, President emeritus - MBCA-International Stars (Eastern Mich.) Now Wi. & Az. 1985 300D Manual 4 speed Green Hen's tooth 1979 MGB triple black Az car nice 1969 back 1/2 of MGB (Az home built trailer) 1991 Volvo 245 Wagon Nice AZ Restored Gold Brick 1983 Jeep CJ7 37,600 Miles Summer use only |
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Cheap out on the fuel and expect to pay for it in the long run.
save $3 or spend thousands on a new engine |
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The owners manual will address this question. Generally it is OK if you don't accellerate hard and you keep your RPMS under 3 or 4K. Everyone likes to believe all kinds of great things about premium gas. The only difference is it resists knock more. But the truth is these threads are worse than oil threads. Read the manual. All cars are not the same. If you like to rabbit stomp all around then run premium.
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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine) 1988 F150 144,000 miles (leaks all the colors of the rainbow) Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra |
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You can always retard the spark to run on regular (87 octane) if the computer doesn't, but you sacrifice performance. As long as there is absolutely no pinging/knocking, you won't damage the engine; knocking is extremely damaging. If you later have a valve job, chances are the head(s) will be resurfaced, which will increase the compression slightly (unless each cylinder chamber-top is honed to compensate) and thus requiring further spark retarding. In the end, it's a trade-off between higher($) gas or lower performance.
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Don't Chrome them; polish them |
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There is no evidence the "computer compensates" and it in fact is NOT designed to do so. This is simply wishful thinking and borders on fantasy to believe so. (I'd like, BTW, to see the "timing retarded" on one of the new distributorless cars--which describes all 1999-2005.)
The typical 6-cyl Mercedes engine is around 180 cu in and develops the same horsepower as an American iron boat anchor engine of around 350 cu in. It takes high compression--and consequently premium fuel--to accomplish this. The V8s are in a similar state of tune. Maybe it's SOP to ignore what American car manufacturers recommend, but you do so very much at your peril with German stuff.
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Kent Christensen Albuquerque '07 GL320CDI, '10 CL550. '01 Porsche Boxster Two BMW motorcycles Last edited by lkchris; 09-14-2008 at 07:01 PM. |
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What do you mean?
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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine) 1988 F150 144,000 miles (leaks all the colors of the rainbow) Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra |
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The computer will sense the knock and retard your spark, so you won't hurt anything. You will lose some power, and mileage.
But its false economy, and really if you are looking to buy a Mercedes and the extra $3 a tank matters...
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1999 SL500 1969 280SE 2023 Ram 1500 2007 Tiara 3200 |
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1999 SL500 1969 280SE 2023 Ram 1500 2007 Tiara 3200 |
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Kent Christensen Albuquerque '07 GL320CDI, '10 CL550. '01 Porsche Boxster Two BMW motorcycles |
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No it's not. They are for minor problems perhaps caused by carbon in cylinder, not for gross changes. This is "legend" that has been built up over the years, mostly again by wishful thinkers. The Mercedes manual would approve regular fuels if your fantasy were correct.
https://www.mbwholesaleparts.com/StarTuned/pdfs/LiquidJune06Star.pdf
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Kent Christensen Albuquerque '07 GL320CDI, '10 CL550. '01 Porsche Boxster Two BMW motorcycles |
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Um well thats how ignition systems work. Thats why modern cars don't ping anymore...
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1999 SL500 1969 280SE 2023 Ram 1500 2007 Tiara 3200 |
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PW: This was an interesting question with a load of OPENIONS. Here is some facts, help yourself, OK. I have three vehicles, all say use 93. A Volvo S-90, a 96 S-320, a 97 SL-320. I've been runing REGULAR sense NEW. VOLVO 80K, S-320 103K, and SL 78K.I use Mobile 1, 10w30 all year round. Volvo=23mpg, S=26 @ 75mph, SL=24 @ 65mph. PW, these are facts, not my openion. Have fun, the older S's are god ole sherman tanks, and the 320's get great milage for such a large car. Mine is the long wheel base model, love it. Ron
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http://i19.photobucket.com/albums/b1...c/GOWIDE-1.jpg 1971 280SL ROADSTER 1988 300CE TWIN TURBO WIDEBODY 1994 E320 CABRIOLET 1999 C43 AMG 2005 G55K AMG 2008 CLK63 AMG BLACK SERIES |
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